Light conductors have different properties with relation to flexibility, light divergence angle, and reception angle depending on what material they are made from. These angles are equally as great for a given light conductor and represent the angle within which the light can be spread from, or collected by, the end of the light conductor. A plastic optical fibre is relatively pliant and generally has a comparatively large light divergence angle. Fibres having a comparatively small light divergence angle are usually manufactured from glass or quartz. However, such fibres are not as pliant as plastic fibres and, furthermore, they are more easily damaged by bending. As an example of the magnitude of the light divergence and light reception angle, it may be stated that in a plastic fibre this is usually between 45.degree. and 90.degree., while the corresponding angle for a glass or quartz fibre is usually only about 15.degree. to 40.degree..
In the G.B. specification No. 1,375,963 there is described an optical cable intended for use in reading an optical information carrier. The cable contains a plurality of fibre conductors, of which the majority are utilized for illuminating the information carrier, and one is utilized for transmitting the light reflected from the carrier to a light-sensitive receiver.
If the information carrier is a display screen, no further illumination thereof is necessary, and thus no fibres are required which lead light to it. Irrespective of how the information carrier is illuminated, however, it is desirable that the so-called reading fibre, i.e. the fibre which transmits light from the information carrier to the light-sensitive receiver, have a small light reception angle. Good resolution is obtained in such a case, which is important for reading information such as bar codes.